Inductive components, for example inductive actuators, are utilized in many fields of application, for example in the field of motor vehicles in control devices as electro-pneumatic converters or proportional valves (magnet valves). These inductive components generally consist of an electromagnet (a coil) and a movable armature, whereby the magnetic field strength that is generated with the electromagnet and that moves the armature is proportional to the current through the electromagnet (the coil).
In several application cases it is necessary to impose a certain magnetic flux and therewith a certain magnetic field strength onto the inductive component, which is supplied by means of a supply voltage (operating voltage); for this, a current with a certain prescribed current strength must flow through the inductive component during a current supply phase. Especially in dynamically very rapid applications (for example the injection process of fuel into the combustion engine of a motor vehicle), it is further necessary to provide a rapid activation and deactivation of the current supply phase, that is to say a rapid switching-on and switching-off of the current through the inductive component (of the coil current).
As is described in the DE 195 33 131 A1, for the rapid switching-on of the current through the inductive component, during a first phase (switching-on phase) of the current supply phase, the inductive component can be subjected to or acted on by a higher voltage than the normal supply voltage (operating voltage), so that a switching-on current flows with a high current strength during the switching-on phase.
The object underlying the invention is to suggest a method for prescribing or specifying the current through an inductive component, wherein an advantageous current progression or course can be realized during the current supply phase, especially at the activation of the current supply phase, in a simple and cost-economical manner with a small number of components.
This object is achieved according to the invention by the feature in the characterizing portion of the patent claim 1. Advantageous embodiments of the method arise from the further patent claims.
For realizing the conceived method, two voltage sources with respective different potentials are provided: a supply voltage source for providing a supply voltage with a certain voltage value (for example 12 V) and a constant voltage source (for example a switching network or combinatorial circuit component) for providing a higher voltage value (for example 55 V) than that of the supply voltage. In order that a rapid rise or increase of the current through the inductive component is achieved after the activation of the current supply phase, the constant voltage source is used for the voltage supply of the inductive component during a first phase of the current supply phase (the switching-on phase), and the supply voltage is used for the voltage supply of the inductive component during a second phase of the current supply phase following the first phase (after the switching-on phase). Two switch-over elements connected in series and a blocking element are provided for the alternating connection of both voltage sources with the inductive component. i.e. for the switching-over of the voltage supply between the two voltage sources, whereby the first switch-over element (for example a field effect transistor FET) is connected with the constant voltage source, the blocking element (for example a blocking diode or a field effect transistor FET) is arranged between the connection of the supply voltage and the junction point of the two switch-over elements, and the second switch-over element (for example a field effect transistor FET) is connected with a connection of the inductive component. For the voltage supply of the inductive component, the constant voltage source is activated at least so long until the current flowing through the inductive component reaches a prescribed current threshold value, that is to say the minimum duration of the first phase of the current supply phase is fixedly specified by the current threshold value; optionally the constant voltage source can still also be applied after reaching the current threshold value, in order to ensure a reliable current flow through the inductive component with the desired current strength even with disadvantageous characteristics of the inductive component. During the second phase of the current supply phase, the current strength of the current flowing through the inductive component can be reduced from a first current value (that is to say from the current threshold value) to a second current value; time point, time characteristic, and the respective applicable current values are selected dependent on the characteristics of the inductive component: the first current value (the current threshold value) is thereby selected as a xe2x80x9ccapture currentxe2x80x9d, so that the armature of the inductive component will be surely xe2x80x9ccapturedxe2x80x9d by the electromagnet, the second current value is selected as a xe2x80x9cholding currentxe2x80x9d, so that the armature of the inductive component will be surely xe2x80x9cheldxe2x80x9d by the electromagnet; the time characteristic or behavior during the transition from the first current value to the second current value is selected so that the characteristics of the inductive component are optimally utilized or improved, for example the current strength of the current flowing through the inductive component is smoothly or glidingly reduced, for example exponentially reduced, in order to ensure a certain injection characteristic of an injection valve; the time point for the switching-over of the current strength is prescribed in connection with an optimization of the characteristics of the system comprising the inductive component (for example an injection valve).
The temporal control of the current flow through the inductive component, that is to say especially the activation and deactivation of the current supply phase, is carried out by a control unit (for example by a microprocessor). In order that a rapid current decrease or fall-off (rapid switching-off of the inductive component) occurs after the deactivation of the current supply phase, the energy stored in the inductive component during the current supply phase must be rapidly dissipated; for this purpose, a switch-off element (for example a switch-off transistor) arranged between the inductive component and the connection of the supply voltage is provided: this switch-off element can either be switched to a highly resistive state and the energy present in the magnet circuit of the inductive component can be transformed into heat upon the deactivation of the current supply phase, whereby the current decrease or fall-off upon the deactivation of the current supply phase can be influenced by means of the height or level of a clamping voltage; or this switch-off element is opened, and a feedback or return flow of the energy stored in the inductive component back into the constant voltage source is carried out by a feedback element (for example a diode) arranged between the inductive component and the connection of the constant voltage source.
A current measuring device connected with the inductive component can be provided for detecting the current flowing through the inductive component during the current supply phase; with this current measuring devicexe2x80x94for example a measuring resistor (shunt), which detects the current flowing through the inductive component during the current supply phase as a measured voltagexe2x80x94the point of reaching the current threshold value (for determining and fixing the minimum duration of the first phase of the current supply phase) can be determined: for this purpose, a certain voltage value is allocated to the current threshold value, whereby this voltage value is compared with the measured voltage determined by the measuring resistor.
The temporal current flow of the current through the inductive component is prescribed by a switching element connected with the inductive component: the activation and deactivation of the current supply phase can be carried out with this switching element; moreover, also the temporal course or progression or the current strength of the current through the inductive component during the current supply phase can be influenced, especially by control activation or driving of the switching element by means of a pulse width modulation (PWM) during the second phase of the current supply phase.
In order to suppress switch-over effects and their consequences on the current flow of the current through the inductive component upon the switching-over of the voltage sources, the pulse width modulation (PWM) can first be activated after a prescribed time interval after the switching-over from the constant voltage to the supply voltage. Hereby also, the reduction of the current strength provided during the second phase of the current supply phase and the time characteristic or behavior in connection with the reduction of the current strength can be prescribed or specified in a simple manner by variation of the pulse duty ratio of the pulse width modulation (PWM).
Advantageously, in the conceived method, a specifying or prescribing of the current through the inductive component is made possible in a simple and cost-economical manner with only a few components, whereby especially a rapid switching-on of the current through the inductive component is made possible; moreover a rapid switching-off of the current through the inductive component and a defined time characteristic or behavior of the current through the inductive component in connection with the switching-on process and in connection with the switching-off process as well as during the current supply phase can be prescribed. As a result of that, the inductive component can be control activated or driven in an optimized manner with respect to time characteristics and power, depending on the application case, and a further operating range with defined (especially constant) characteristics can be specified or established.